In line with the development of optical technologies in recent years, various technologies for display devices such as plasma display panels (PDPs), liquid crystal displays (LCDs), organic electroluminescent displays (OEDs) and the like, to replace cathode-ray tubes (CRT), have been suggested, and have become commercially available. Meanwhile, various polymer films such as polarizing films, polarizing protective films, retardation films, light guiding plates, and plastic substrates are being used in such display devices. Characteristics required for materials used in such display devices have tended to be further enhanced.
Meanwhile, in polarizing plates currently used in image display devices such as liquid crystal display devices, triacetyl cellulose films (hereinafter, referred to as TAC films) are commonly used as protective films for protecting polyvinyl alcohol polarizers. However, since the TAC film has insufficient moisture resistance and heat resistance properties, characteristics of the polarizing plates such as a degree of polarization or color properties may be deteriorated due to the deformation of the film in the case of uses thereof under conditions of high temperature and high humidity. Therefore, of late, a method of using a transparent acrylic resin film having superior moisture resistance and heat resistance properties as a material of a polarizer protective film, instead of the use of the TAC film, has been suggested.
In addition, a technology of adding an ultraviolet absorber to such an acrylic film to provide ultraviolet light absorbing functions, thereby preventing a polarizer from being deteriorated by ultraviolet light, has been proposed. In the case of an acrylic film according to the related art, it is known that a benzotriazole-based compound, a benzophenone-based compound, a benzotriazine-based compound, a cyano acrylate-based compound, a salicylic acid-based compound or the like may be used as the ultraviolet absorber.
However, since a majority of known ultraviolet absorbers may decompose during a high temperature processing operation, ultraviolet light absorbing capability may be deteriorated and further, a resin and a film may be yellowed due to pyrolysis of the ultraviolet absorbers.
In particular, since the benzotriazine-based compound may have a high degree of absorptivity in the ultraviolet B region (315 nm to 280 nm) but have a low degree of absorptivity in the ultraviolet A region (400 nm to 315 nm), an excessive amount of the benzotriazine-based compound needs to be added. However, when an excessive amount of the ultraviolet absorber is added as described above, in a case in which acrylic resin melted by receiving high temperature pressure by an extruder during a process of manufacturing an acrylic film is suddenly cooled down in a casting-rolling process after passing through a T-die, a migration phenomenon, a phenomenon in which the ultraviolet absorber may decompose and be discharged outside of the film to be stained on a casting roll, may be excessively generated. As a result, the pyrolyzed ultraviolet absorber may also be stained on the film, thereby causing defects in the exterior of the film.
Moreover, since ultraviolet absorbers well known in the art may have low degrees of molecular weight and low glass transition temperatures, in a case in which a large quantity of such ultraviolet absorbers are added, a glass transition temperature of a resin composition may be significantly lowered, such that heat resistance properties may be degraded or optical properties of an optical film may be negatively influenced thereby.
Thus, the development of technologies allowing for the manufacturing an optical film having superior ultraviolet light absorptivity and a high glass transition temperature (Tg) while not allowing the occurrence of coloring and contamination, has been requested.